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Designing intuitive user experiences for non-traditional user flows, such as checkout, can be complicated. In order to solve this, most modern sites provide a wizard to guide the user. The wizard lists breaks the flow into pieces, lists them for the user, and displays their current progress. They help the user understand where they are in the process intuitively.

One such application I recently worked on had a navbar designed with the usual logo on the left, some other text on the right, and something like this in the middle for the first page:

On the second page, the the left and right were the same but the middle part of the navbar was different:

The quantity of steps was not certain yet. It might end up being compressed to two steps or possibly being expanded to a fourth optional step before this went into production.

Now we could obviously write this the copy/paste way into a new file for each step nav-bar-step1, nav-bar-step2, nav-bar-step3, but who wants to try to keep that all in sync? We want to make our code more flexible and have fewer files to manage, while at the same time making this first version of the product simple and fast to get started with.

This is a good opportunity to explore computed properties and components in Ember.js. In Ember, a component is a view that is isolated from other views. It has its own data and can be reused in multiple other places. It cannot access properties outside its own scope; properties from the parent view must be explicitly passed in. We’re going to build one together for this navigation element. We’ll describe computed properties in just a moment.

In this example, we will be passing a static state for the steps in the nav-bar, which will be defined in each call to render the component. You will be able to find additional examples online explaining this passing model properties into the component.

Version 1 (Using good ol’ jQuery)

Hop over to your project directory in the terminal and run the command to generate a component. (Don’t forget it must have a dash in the component name. You must already have a project started and have Ember-CLI installed.):

ember generate component nav-bar

Call the component to be rendered in the handlebars (.hbs) file for the templates where you want to display this component using {{nav-bar}}. Open the component’s .hbs file and add in your html. We’ll use a ul in our example, but you can style this however you like. You just need to define something so you can see a change in the page tell that the value is getting passed.

In this example, I’ve added some CSS to distinguish between the three states each step could be in. The default step state is upcoming or in the future. For the step they are currently on, I will use a class step-active. Likewise, for completed steps I will use the class step-complete.

To communicate this to Ember, first we’ll be calling for the component to be rendered, then passing it’s properties. For the step they are currently on, pass the id step-2 to the component property stepActive. Likewise, for the past steps the user has already completed, pass that id step-1 to the component property stepComplete. Go to the parent template’s .hbs file and set each of the variables in your call to the component. {{nav-bar stepActive="step-2" stepComplete="step-1”}}.

Open the .js file for your component. You will need to define variables here that will catch the values we just passed in. We will be defining them in didInsertElement() not init() because we’re using jQuery in this first version of the example. To do this, jQuery must have the component’s html rendered into the DOM to attach properly. More info about these predefined functions at the Ember.js Guides.

Inside that didInsertElement() function, save each property in a variable var activeStep = this.get('stepActive');. You could throw in a simple console.log("activeStep: " + activeStep); statement next to ensure that everything is connecting properly.

Finally, we want to assign those css classes to the correct DOM elements. I like to check my work with color. Add something to your CSS file like:

.step-active {
background-color: red;
}

Then put in the code to assign the class to the correct element if that property has been passed in to that didInsertElement() function.

Version 2: (Using Ember’s Computed Properties)

Now this works… but it’s really not leveraging Ember’s abilities. It’s basically the same as if we wrote some functions at document.ready. This is a good place to start, especially if you are already familiar with jQuery, but let’s use this page to show another strategy we could use.

Let’s refactor this to use Ember’s computed properties. Computed properties in Ember are a great way to allow you to update view data on the fly. They allow you to essentially declare a function that is accessed like a property. Although we will not allow the user to change the value of the properties in this example, computed properties allow your component to react to data changes (such as a model property).

We are going to create a component for each step in our nav-bar. The nav-bar component will call the navbar-step component once for each step and pass in the properties it needs. First, let’s create the new component:

ember generate component navbar-step

In navbar-step.hbs insert the code for one step.

<li id="step-1"><span class="step">1</span> Information </li>

After changing the number and text to be properties and removing the surrounding li tags, it becomes:

<span class="step">{{stepNumber}}</span> {{stepLabel}}

We won’t need that id anymore (we were only using it for targeting). We will need that li back rather than the default component tag which is div so go to the new component’s navbar-step.js and set that using tagName: 'li'.

Go to your original component, nav-bar.hbs, and call each step using the step component. We will need to pass stepActive and stepComplete through as a property. (There are other ways to handle this if it gets more complex, such as using a service, that won’t be covered in this blog post.) I have switched these to just the number instead of the class name.

Here comes the exciting part, the new computed properties. Go to the new component’s navbar-step.js file and pass the property through and create the new computed properties. (You’ll need one for each property: isStepActive and isStepComplete.)